Investigation and prediction of optical properties of alumina nanofluids with different aggregation properties. (May 2016)

• Record Type: Journal Article
• Authors: Song, Dongxing; Wang, Yechun; Jing, Dengwei; Geng, Jiafeng
• Is Part Of: International journal of heat and mass transfer. Volume 96(2016:May)
• Page Start: 430
• Page End: 437
• Publication Date: 2016-05
• Subjects: Particle size distribution -- Absorption coefficient -- Mie scattering theory -- Smallest sphere enclosing diameter; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2016.01.049
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Alumina nanofluids with different aggregation properties have been obtained. Relation between the aggregating and optical properties were fully investigated. Mie scattering theory can reasonably describe the experimental results. Smallest sphere enclosing diameter is proposed to improve the Mie theory. Abstract: Nanofluids as thermal absorption media or optical filters have showed great potential for application in direct absorption solar collector or hybrid photovoltaic/thermal (PV/T) collectors. Due to their nanoscale size and high surface energy, particles in nanofluid have a great tendency to aggregate into large secondary agglomerate, even in the presence of the anti-agglomeration agent, which could in turn lead to significant change in the thermal and optical properties of the nanofluid. However, rare work has been carried out to investigate the relation between the aggregation and optical properties of the nanofluid, which in our view, is of great importance for the enhanced performance of the nanofluid in solar collectors. In this study, taken alumina nanofluids with controlled particle aggregation properties as example, we were able to investigate the underlying correlation between the size distribution of the aggregate in nanofluid and their resulting absorption coefficients. It was found that inhibited aggregation and resultant smaller aggregated particle size could lead to larger absorption coefficient. Both Rayleigh scattering and Mie scattering theories have been attempted to predict the optical properties of the nanofluid after particle aggregation. The results indicate that values obtained by Rayleigh scattering theory are several orders higher than experimental values but that predicted by Mie scattering theory can reasonably match with the experimental results. Specially, it was demonstrated that by introducing the projected areas of the nanoparticle aggregate corresponding to smallest sphere enclosing diameter, more accurate absorption coefficient prediction based on Mie theory can be obtained. Our study is expected to provide a valuable guidance for the regulation of the optical properties of nanofluids and to improve their performance in solar collectors.